The present invention relates to an energy absorbing device, and more particularly to an energy absorbing device in a (motor) vehicle bumper system to absorb impact energy originating from a car accident.
Customarily, there are several different requirements for optimally-functioning bumper systems in vehicles. Presently the car manufactures operate with three levels of impactxe2x80x94low up to 4-8 km/h, intermediate from 4-8 to 16 km/h and finally impacts at a speed exceeding 16 km/h.
Normally, the impact at the low and the intermediate speeds is taken care of by the bumper member itself and a reversible or non-reversible energy absorbing element, usually located between the bumper member and extending to or into the longitudinal members of the vehicle. The impact energy of a collision at a speed over 16 km/h will finally mostly be absorbed by deformation of one or more front/rear side members of the vehicle frame.
The energy absorbing elements may be a thin-walled folding member which can be filled with foam or other resilient material. The drawback of filling the member is that it is then not totally compressible due to the solid block being made. Furthermore, it also has the drawback of having a varying force over the displacement due to the varying resistance when making folds.
Other design principles commonly used are: absorbing energy by inverting a tube wall; absorbing energy by means of pressing a tube through a restriction, thus reducing the tube diameter; pressing a fluid or a wax through apertures in a cylinder or a piston, typical in a reversible system; and expanding the diameter of a tube by forcing a substantially solid member through the tube. These solutions often have the drawback of having to provide a flange for attachment to the side member.
It is known that these folding membersxe2x80x94customarily based on relatively small diameter tubesxe2x80x94may be unstable and tend to bend out when subjected to an impact load that is not co-axial with the member or arising at an angle to the member. This is important since it is well known that a large portion of front and rear vehicle impacts arise at an angle to the vehicle""s longitudinal axis and thus result in non-axial loads. It is also known that many of these members lock solid when subjected to a non-axial load or a load arising at an angle to the member.
Furthermore, from JP 60121147 it is known to absorb impact energy by a special design of a bumper-attaching member comprising several elongated holes having a width smaller than the diameter of fastening members (bolts) extending through the holes. Upon a moderate speed crash of the vehicle, the received impact force will be transferred via the fastening bolts into the edges of the holes. The impact energy will then be absorbed by widening of the holes due to successive movement of the bolts along the holes. The shortcomings of this solution are apparently the limited amount of energy that can be absorbed by a simple deformation/enlarging of the holes. A possible compensation for this drawback requires a substantial increase of the wall thickness of the attaching member and, thus, increase in weight and costs of the device, effecting negatively both performance and price for the vehicle.
Consequently, it is an object of the present invention to provide a novel low weight energy absorbing device that exhibits substantially improved absorption of impact energy. Another object of the invention is to provide a low cost and easily assembled energy absorbing device. Still another object of the invention is to provide an energy absorbing device with no limits regarding the applied material improving the total strength of the bumper beam (system).
These and other objects of the present invention are achieved by the energy absorbing device as described and defined below, including the preferred embodiments of the device.